The α‐effect in micelles: Nucleophilic substitution reaction of p‐nitrophenyl acetate with N‐phenylbenzohydroxamate ion

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with p‐chlorophenoxide (4‐ClC₆H₄O^?) and N‐phenylbenzohydroxamate (C₆H₅CON(C₆H₅)O^?) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij‐35) surfactants has been studied. The k_obs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and α‐effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26–31, 2006     

Kinetics of Catalytic Hydrogenation of 5‐Hydroxymethylfurfural to 2,5‐bis‐Hydroxymethylfuran in Aqueous Solution over Ru/C

5‐Hydroxymethylfurfural (5‐HMF) is a cellulosic product of the hydrolysis of biomass, and it is widely considered for the production of several interesting chemicals and derivatives. In the present work, catalytic hydrogenation of 5‐hydroxymethylfurfural to 2,5‐bis‐hydroxymethylfuran was investigated using 5% Ru/C in the aqueous phase. Kinetic data were experimentally obtained over a wide range of temperatures (313–343 K), H₂ partial pressure (0.69–2.07 MPa), initial HMF concentration (19.8–59.5 mM), and catalyst loading (0.3–0.7 kg/m³) in a three‐phase slurry reactor. Disappearance of initial 5‐HMF concentrations was modeled using the power law and Langmuir–Hinshelwood–Hougen–Watson models. A model based on the competitive adsorption of molecular H₂ and HMF was proposed. It is presumed that surface reaction between nondissociatively chemisorbed H₂ and 5‐HMF was rate determining. This model provided the best fit for the kinetic data. From the Arrhenius equation, the activation energy for the surface reaction was found to be 104.9 kJ/mol.     

Recycling of uranium containing alkaline waste solution generated in the preparation of UO3 microspheres by the internal gelation process

Summary A recent study has indicated the feasibility of recycling of chemicals from alkaline waste generated in the preparation of UO₃ microspheres by the internal gelation process. Present paper investigates the recycle process, the volume of the secondary uranium waste. Result shows that prior to start the recycle process, the waste solution should be freed from uranium by ion-exchange. Optimized experimental condition to achieve maximum reduction in the volume of uranium based waste is discussed.     

Removal of plutonium from carbonate medium using titania microspheres prepared by sol-gel route

Spherical beads of titania were prepared by a sol-gel route. During the preparation a cationic surfactant was added in the feed broth to modify the surface characteristics of the microspheres. The absorption behavior of Pu(IV) from carbonate medium on these microspheres was studied by batch experiments. Loading and elution behavior of Pu(IV) on a bed of titania microspheres was studied and the practical capacity was determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of pressure on the electrical resistivity and thermoelectric power of the compounds Ba(Pb1-xBi x )O3 and K y Ba1-yPb0.5Cu0.5O3-x

High pressure studies on the electrical resistivity and thermoelectric power of BaPb_1-xBi _x O₃ and K _y Ba_1-yPb_0.5Cu_0.5O_3-x show that many compounds in these systems exhibit qualitatively the same type of behaviour as observed in the superconducting oxides (La, Sr)CuO₄ and YBa₂Cu₃O_7-x. The compounds K _y Ba_1-yPb_0.5Cu_0.5O_3-x show temperature-independent resistivity over a wide range of temperatures, but are not found to be superconducting down to 77 K.     

High pressure studies on layered semiconductor germanium sulphide single crystals grown using different techniques

Abstract

Single crystals of GeS have been grown by DVT and CVT techniques. The grown crystals have been characterised by XRD. The band gaps E_g have been determined from the optical absorption studies. The results of simultaneous thermoelectric power and resistivity measurements up to 8 GPa on single crystals of GeS grown using different techniques are reported here. The measurements show a decrease in a.c. resistivity with increase in frequency up to 66.6 kHz. This behavior can be attributed to the presence of defects and impurity atoms in the semiconductor, which can contribute to conduction by the hopping process.     

Effect of pressure on electrical resistance of WSe<Subscript>2</Subscript> single crystal

The results of electrical resistance measurements under pressure on single crystals of WSe₂ are reported. Measurements up to 8.5 GPa are carried out using Bridgman anvil set up and beyond it using diamond anvil cell (DAC) up to a pressure of 27 GPa. There is no clear indication of any phase transition till the highest pressure is reached in these measurements.     

Growth and high pressure studies of zirconium sulphoselenide single crystals

Transition metal trichalcogenides are well suited for extreme pressure lubrication. These materials being semiconducting and of layered structure may undergo structural and electronic transition under pressure. In this paper authors reported the details about synthesis and characterization of zirconium sulphoselenide single crystals. The chemical vapour transport technique was used for the growth of zirconium sulphoselenide single crystals. The energy dispersive analysis by X-ray (EDAX) gave the confirmation about the stoichiometry of the as-grown crystals and other structural characterizations were accomplished by X-ray diffraction (XRD) study. The variation of electrical resistance was monitored in a Bridgman opposed anvil set-up up to 8 GPa pressure to identify the occurrence of any structural transition. These crystals do not possess any structural transitions upto the pressure limit examined.     

Efficient Entrapment of Dye in Hollow Silica Nanoparticles: Direct Evidence Using Fluorescence Spectroscopy

Using hollow silica nanoparticles we demonstrate a simple and highly efficient way of removing hydrophilic dye (Rhodamine B) from water by encapsulation within these hollow spheres. The hollow silica spheres were obtained by using a surfactant templated procedure. Using fluorescence spectroscopy, we also show the evidence of the dye being absorbed within the hollow core of the silica shell (which is crucial for many applications) and differentiate from the adsorption of dye on the surface of the silica shell. It was found that that up to 94 % of the hydrophilic dye could be entrapped using these hollow shells within 72 h of exposure. Fluorescence spectroscopy shows a red shift in the dye encapsulated in the hollow silica which is due to aggregation of the dye and enables us to follow quantitatively the uptake of the dye molecules by the silica shells with time. The evidence for the encapsulation of the dye in these hollow spheres was reinforced by carrying out a comparative study, using solid silica particles.